Preheat oven to 400 degrees.
In large bowl, combine self-rising cornmeal mix, sugar (if using), yellow corn kernels (or cream-style corn), sharp cheddar cheese, jarred diced jalapeno peppers, chopped white onions (if using) 2 beaten eggs, and buttermilk.
NOTE: Use two small or medium eggs. Or use ONE large egg.
Stir until well combined. Set aside.
Grease 9" cast iron skillet (or other bake ware) with vegetable oil. On top of stove, heat greased skillet over low-medium heat... until oil is sizzling hot (but not smoking).
Greased skillet is hot enough when a small drop of batter sizzles when dropped in hot oil. WARNING: Hot oil may pop out of skillet. Wear an oven mitt and keep face away from skillet with hot oil.
Turn heat off. Carefully pour batter into hot greased skillet. Smooth evenly with back of spoon.
Use oven mitt to carefully place skillet into preheated oven. Reduce temperature to 375 degrees.
Bake 20 to 25 minutes or until toothpick or knife inserted in center comes out clean.